The invention relates generally to moisture absorbent articles such as diapers, incontinence articles, feminine hygiene products such as tampons and pads, absorbent dressings, pads for food packaging, and the like. More particularly, the invention relates to compositions of matter for use in disposable articles for the absorption of water, urine, blood, and other fluids and to an absorbent pouch for storing food products.
There has been abundant activity in recent years in the area of absorbent compositions and articles incorporating the same, such as diapers, incontinence articles, feminine hygiene products, absorbent dressings, and food packaging. The prior art teaches the use of water insoluble crosslinked polymeric substances which possess the ability to absorb large quantities of fluids relative to their own weight and volume. Such polymeric materials include starch graft copolymers, crosslinked salts of acrylic acid, in particular sodium polyacrylate, and crosslinked cellulose derivatives, including crosslinked sodium carboxymethylcellulose (CMC). Many of the listed polymers are not approved as safe for incorporation into or contact with food products. Some types of non-crosslinked CMC, however, have been approved for use in food applications.
It is well known that non-crosslinked cellulose derivatives, such as from CMC, hydroxyethylcellulose, methylcellulose, and hydroxypropylmethylcellulose, produce a soft gel when hydrated, having low gel strength, and an unpleasant slippery (slime like) feel. This mitigates against their use, particularly in food packaging applications. Further, the gel formed from such materials can produce a gel block effect when used in absorbent articles. Gel block effect refers to the tendency of a gel to form around the masses of CMC particles, thus slowing or preventing fluid from being taken up by the internally- situated particles. This minimizes the usable absorbent capacity of the material.
The gel block effect can be minimized by using crosslinked CMC. This also has the effect of strengthening the gel. However, the cost of chemically crosslinked CMC in granular form has prevented its commercial development. Its use in food packaging would also require formal FDA approval, because of the chemical processes involved in preparing the crosslinked material.
Clays, and other mineral compositions such as diatomaceous earth, are known for their aqueous liquid absorbing properties. However, the use of clay, alone, may be problematic for some applications, due to its colloidal, dispersive properties in water. To this effect, the prior art teaches the use of clays in combination with other ingredients such as polymers. For example, U.S. Pat. No. 3,935,363 to Burkholder et al. teaches that clay minerals have enhanced water absorbing properties when flocculated into granular aggregates using small amounts of an inorganic salt solution and/or a water soluble polymeric flocculating agent such as polyacrylic acid and then dried. U.S. Pat. No. 4,914,066 to Woodrum teaches a blend of bentonite clay ( greater than 85%) and a water swellable but water insoluble organic polymeric hydrocolloid for improved absorbency in cat litter applications. U.S. Pat. No. 4,615,923 to Marx discloses a dry blend of kieselguhr (diatomaceous earth) with organic gel formers (CMC, starch, dextrose, gelatin, etc.) for use in absorbent pads for food packaging.
Another absorbent composition is taught in U.S. Pat. No. 4,454,055 to Richman et al. Which discloses a dry, water swellable absorbent composition comprising a blend of a water insoluble absorbent polymer such as an ionically complexed anionic polyelectrolyte, a polysaccharide graft polymer, or a covalently linked anionic polyelectrolyte with an extender material selected from non-crosslinked cellulose derivatives, starch, certain clays and materials, and mixtures thereof The extender material(s) comprise from 1 to 75% by weight of the blend. It is stated that these blends provide significantly greater absorbency than would be expected from is the sum of the individual absorbencies of the ingredients.
Meat and poultry food products are typically sold in a supporting tray that is overwrapped by a transparent plastic film, enabling visual inspection of the food products. To avoid the uncontrolled accumulation of exuded fluids from the food products, an absorbent pad is often placed in the supporting tray. The simplest types of absorbent pads for absorbing food product fluids consist essentially of a bundle of sheets of absorbent paper with or without a sheet of plastic film below the bundle. Another sheet of plastic film may also be placed over the bundle of paper sheets. One or both of the sheets of plastic film typically are perforated or are otherwise fluid pervious.
In some configurations, the paper sheets have been replaced with a more absorbent material. For example, U.S. Pat. Nos. 4,940,621, 5,022,945, and 5,055,332 to Rhodes disclose a structure incorporating cellulose pulp fibers alone or mixed with polyolefin fibers and possibly including superabsorbent granules dispersed and held within the fiber structure. U.S. Pat. No. 5,176,930 to Kannankeril describes an absorbent pad comprising a mat of liquid absorbent material (cellulose fluff) enclosed between upper and lower sheets of plastic film with the lower sheet perforated to allow fluid to flow into the pad from the under side by capillary action. Another change to increase the absorbency of a pad taught in U.S. Pat. No. 5,176,930 involves a structural change in which a portion of the intermediate layer is allowed to extend to the periphery of the pad so as to contact fluid and wick it into the absorbent layers of the pad.
A disadvantage of the above discussed types of absorbent pads is that cellulose fluff has a low absorbency (up to about 3.5 grams per gram) and does not retain moisture under pressure. In addition these types of pads tend to break up in use so that paper, fluff, and film may adhere to the food and leakage may occur from the packages.
One way to solve the problem of leakage has been the incorporation of absorbent pads into plastic bags as described in U.S. Pat. No. 4,742,908 to Thomas, Jr. et al. and U.S. Pat. No. 4,815,590 to Pepplatt et al., both of which teach bags having an absorbent pad inserted mechanically into the bag and attached to one panel of the bag by thermal welding or glue or other adhesive means. However, attaching the pads to the bag increases the cost of production.
It is an object of the present invention to provide new dry, solid, fluid swellable, fluid absorbing compositions of matter that have improved absorbency and gel strength properties, and present minimum gel block effect.
It is another object of the present invention to provide new fluid absorbing compositions of matter that exhibit a minimum of syneresis.
It is a further object of the present invention to provide structures for absorbent articles prepared from the materials of the invention.
Yet another object of the present invention is to provide a new type of package incorporating food safety approved absorbents which incorporates an absorbent panel as part of the package. Such a package could be used for packaging of fresh poultry, meats, seafood, fresh cut fruits, vegetables, and other products, and will allow extended shelf life of the foods packaged therein under conditions appropriate for the particular food stuff.
In order to achieve the above and other objects, an absorbent material is provided which is a blend of at least one non-crosslinked gel forming polymer, at least one clay, and at least one trivalent cation. In addition, the composition can include diatomaceous earth in place of some of the clay. Further, natural gums such as xanthan, guars, and alginates can be added as can inorganic buffers. The absorbency of the blend exceeds the sum of the absorbencies of the individual components of the blend.
The gel formed as a result of absorption of fluid has high gel strength and exhibits a low level of gel block effect. In the case of food packaging applications, all components of the blend can be selected from materials known to be regulated by FDA as GRAS (generally regarded as safe) for incorporation in foods. The absorbent material of this invention is believed to be the only food safe absorbent that also provides the necessary gel strength and absorbency criteria for food packaging applications.
The non-crosslinked gel forming polymer can include cellulose derivatives, such as CMC and salts thereof, hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and also gelatinized starches, gelatin, dextrose, and the like, and mixtures thereof. The clay component can include attapulgite, montmorillonite (including bentonite clays), hectorite, sericite, kaolin, and mixtures thereof. A portion of the clay can be replaced with diatomaceous earth. The trivalent cation can be derived from aluminum sulfate, potassium aluminum sulfate, and other soluble salts of trivalent metal ions such as aluminum, chromium, and the like. The inorganic buffer can be one such as sodium carbonate (soda ash), sodium hexametaphosphate, sodium tripolyphosphate, and the like.
A method of agglomeration of the blend is described which enhances the rate of absorbency as well as increases the maximum total absorbency of the material and improves the strength of the gel formed on hydration of the material.
Structures for absorbent articles prepared from the absorbent material are described.
A new type of package for fresh foods is described which incorporates an absorbent panel that contains an absorbent material such as the absorbent material of the present invention. The package comprises a two walled bag or pouch wherein one wall is a moisture impervious thermoplastic such as polyethylene, having a desired oxygen transmission rate (OTR). The second, absorbent, wall has two plies with the outer ply being moisture impervious and made out of polyester, for example, and the inner ply being permeable to fluids and wherein an absorbent material, such as that disclosed herein, is trapped between the two plies. The two plies of the second wall are heat sealed together in a pattern so that pockets or cells are created containing the absorbent material. The bag is heat sealed around three sides and the fourth side or end can be folded over and heat sealed to the bag to seal the package.